Algae resistant roofing granules with controlled algaecide leaching rates, algae resistant shingles, and process for producing same

ABSTRACT

Algae-resistant roofing granules are formed by extruding a mixture of mineral particles and a binder to form porous granule bodies, and algaecide is distributed in the pores. Release of the algaecide is controlled by the structure of the granules.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a division of pending U.S. application Ser.No. 12/877,921, filed Sep. 8, 2010, which is a division of U.S.application Ser. No. 10/600,809 filed Jun. 20, 2003, now U.S. Pat. No.7,811,630.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to asphalt roofing shingles, protectivegranules for such shingles, and processes for makings such granules andshingles.

2. Brief Description of the Prior Art

Pigment-coated mineral rocks are commonly used as color granules inroofing applications to provide aesthetic as well as protectivefunctions to the asphalt shingles. Dark blotches or streaks sometimesappear on the surfaces of asphalt shingles, especially in warmer humidclimates, as a result of the growth of algae and other microorganisms.The predominant species responsible is Gloeocapsa magma, a blue greenalgae. Eventually, severe discoloration of the entire roof can occur.

Various methods have been used in an attempt to remedy the roofingdiscoloration. For example, topical treatments with organic algaecideshave been used. However, such topical treatments are usually effectiveonly for a short term, typically one to two years. Another approach isto add algaecidal metal oxides to the color granule coatings. Thisapproach is likely to provide longer protection, for example, as long asten years.

Companies, including Minnesota Mining and Manufacturing (3M) and GAFMaterials Corporation/ISP Mineral Products Inc., have commercializedseveral algaecide granules that are effective in inhibiting algaegrowth.

A common method used to prepare algae-resistant (AR) roofing granulesgenerally involves two major steps. In the first step, metal oxides suchas cuprous oxide and/or zinc oxide are added to a clay and alkali metalsilicate mixture that in turn is used to coat crushed mineral rocks. Themixture is rendered insoluble on the rock surfaces by firing at hightemperatures, such as about 500° C., to provide a ceramic coating. Inthe second step, the oxides covered rocks are coated with various colorpigments to form colored algae-resistant roofing granules. Thealgae-resistant granules, alone, or in a mixture with conventionalgranules, are then used in the manufacture of asphalt shingles usingconventional techniques. The presence of the algae-resistant granulesconfers algae-resistance on the shingles.

Roofing granules typically comprise crushed and screened mineralmaterials, which are subsequently coated with a binder containing one ormore coloring pigments, such as suitable metal oxides. The binder can bea soluble alkaline silicate that is subsequently insolubilized by heator by chemical reaction, such as by reaction between an acidic materialand the alkaline silicate, resulting in an insoluble colored coating onthe mineral particles.

U.S. Pat. No. 3,507,676 discloses roofing granules containing zinc, zincoxide, or zinc sulfide, as an algaecide and fungicide.

Algae-resistant shingles are disclosed, for example, in U.S. Pat. No.5,356,664 assigned to Minnesota Mining and Manufacturing Co., whichdiscloses the use of a blend of algae-resistant granules andnon-algae-resistant granules. The algae-resistant granules have an innerceramic coating comprising cuprous oxide and an outer seal coatinginitially devoid of copper.

There is a continuing need for algae-resistant roofing products havingalgaecide leaching rates that can be controlled so that the roofingproducts can be tailored for specific local conditions.

SUMMARY OF THE INVENTION

The present invention provides algae-resistant roofing granules havingalgaecide leaching rates that can be easily controlled, and asphaltshingle roofing products incorporating such algae-resistant roofinggranules.

The present invention employs mineral particles to form algae-resistantroofing granules. In contrast to prior processes for formingalgae-resistant granules, which typically use crushing to achievemineral material having an average size and size range suitable for usein manufacturing asphalt roofing shingles, the process of the presentinvention employs mineral particles having an average size smaller thanthat suitable for use in manufacturing asphalt roofing shingles. Thesemineral particles are aggregated to provide suitably sized roofinggranules.

The mineral particles are treated with a suitable binder, such as a claybinder, and the mixture of mineral particles and binder is processedusing a suitable mechanical technique, such as extrusion, to form porousgranule bodies that are of a size suitable for use in manufacturingasphalt roofing shingles, such as from sub-millimeter size up to about 2mm. The granule bodies can be fired or sintered to provide physicalstrength.

The binder and the mechanical forming process are selected to providealgae-resistant roofing granules that are sufficiently porous to permitleaching of algaecide to provide the desired algaecidal properties.Porosity is preferably between about 3% and about 30% by volume.

Several techniques can be used to introduce algaecides into the granulebodies. Metal oxides, including cuprous oxide and zinc oxide, areespecially preferred as inorganic algaecides, because of their favorablecost/performance aspects. Inorganic algaecides that are only slightlysoluble in water are preferred, so that such algaecides will slowlyleach from the granules thereby providing algae-resistance to thegranules and the roofing products in which such granules have beenembedded.

The algaecide can be optionally included in the mixture of mineralparticles and binder before the granule bodies are formed.

Alternatively, the algaecide can be incorporated after the granulebodies have been formed. For example, the granule bodies can beoptionally coated with at least one intermediate coating binder, such asan alkali metal silicate, optionally including one or more algaecides.The intermediate coating binder is preferably different from thatemployed in forming the granule bodies. The intermediate coating bindercan then be optionally cured, such as by chemical treatment or heattreatment (e.g. firing).

In another alternative, the porous granule bodies are immersed in analgaecide solution, such as an aqueous solution of a soluble coppersalt, such as cupric chloride, and the algaecide solution is drawn intothe porous granule bodies by capillary action. Subsequently, thealgaecide solution-laden granule bodies can be treated, as by heating,to dry the granule bodies, and to convert the soluble algaecide into aless soluble form. For example, the granule bodies can be heatedaccording to a predetermined protocol to convert a soluble copper salt,such as cupric nitrate, to a copper oxide, such as cuprous oxide.

In another alternative for incorporating the algaecide in the porousgranule bodies, the porous granule bodies are immersed in a slurryformed with fine particles of an algaecide, such as cuprous oxide, andthe slurry is drawn into the pores of the granule bodies by capillaryaction. In the alternative, pressure or vacuum can be applied to forceor draw the algaecide into the pores of the granule bodies. Thealgaecide-laden granule bodies are then dried.

Various combinations of the above-described alternatives for introducingalgaecide into and/or on the granule bodies can also be employed toachieve desired algaecide leach rates and leaching profiles. Forexample, a first proportion of a first algaecide can be incorporated inthe binder used to aggregate the mineral particles, and a secondalgaecide can be introduced into pores formed in the granule bodies.

The granule bodies can be optionally coated with a colorant coating, thecolorant coating including a binder, such as an alkali metal silicate,clay, and one or more colorant materials, such as a suitable metal oxidepigment. The colorant coating can then be insolubilized.

Preferably, the intermediate particles are coated with the optionalintermediate coating and the colorant coating before the binder isinsolubilized.

By adjusting the porosity of the granule bodies, and the nature andamounts of algaecide in the intermediate particle binder and theintermediate coating binder, the algaecidal resistance properties of thealgae-resistant granules can be varied.

Preferably, the metal oxide concentration ranges from 0.1% to 7% of thetotal granules weight.

The algae-resistant granules prepared according to the process of thepresent invention can be employed in the manufacture of algae-resistantroofing products, such as algae-resistant asphalt shingles. Thealgae-resistant granules of the present invention can be mixed withconventional roofing granules, and the granule mixture can be embeddedin the surface of bituminous roofing products using conventionalmethods. Alternatively, the algae-resistant granules of the presentinvention can be substituted for conventional roofing granules inmanufacture of bituminous roofing products, such as asphalt roofingshingles, to provide those roofing products with algae-resistance.

It is thus an object of the present invention to provide a process forpreparing AR roofing granules having a controllable algaecide-leachingrate.

It is also an object of the present invention to provide a process forpreparing roofing shingles to have algae-resistance that can becustomized to the specific geographic region in which the shingles areintended to be used.

It is a further object of the present invention to providealgae-resistant roofing granules having controllable levels of algaeciderelease.

It is a further object of the present invention to provide algaeresistant asphalt shingles.

These and other objects of the invention will become apparent throughthe following description and claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of a first type of analgae-resistant granule prepared according to the process of the presentinvention.

FIG. 2 is a schematic representation of a second type of analgae-resistant granule prepared according to the process of the presentinvention.

FIG. 3 is a schematic representation of a third type of analgae-resistant granule prepared according to the process of the presentinvention.

FIG. 4 is a schematic representation of the process of the presentinvention.

FIG. 5 is an electron micrograph showing a cross-sectional view of afirst algae-resistant granule prepared according to the process of thepresent invention.

FIG. 6 is an electron micrograph showing a cross-sectional view of asecond algae-resistant granule prepared according to the process of thepresent invention.

DETAILED DESCRIPTION

The mineral particles employed in the process of the present inventionare preferably chemically inert materials. The mineral particlespreferably have an average particle size of from about 0.1 μm to about40 μm, and more preferably from about 0.25 μm to about 20 μm. Stone dustcan be employed as the source of the mineral particles in the process ofthe present invention. Stone dust is a natural aggregate produced as aby-product of quarrying, stone crushing, machining operations, andsimilar operations. In particular, dust from limestone, marble, syenite,diabase, greystone, quartz, slate, trap rock, and/or basalt can be used.Ceramic materials, such as silicon carbide and aluminum oxide ofsuitable dimensions can also be used.

The binder employed in the process of the present invention ispreferably a heat reactive aluminosilicate material, such as clay,preferably, kaolin. The bodies are preferably formed from a mixture ofmineral particles and binder, ranging from about 95% by weight binder toless than about 10% by weight binder, and the bodies preferably areformed from a mixture that includes from about 10% to 40% by weightbinder.

When the formed granules are fired at an elevated temperature, such asat least 800 degrees C., and preferably at 1,000 to 1,200 degrees C.,the clay binder densifies to form strong particles.

Examples of clays that can be employed in the process of the presentinvention include kaolin, other aluminosilicate clays, Dover clay,bentonite clay, etc.

The algae-resistant roofing granules of the present invention can becolored using conventional coatings pigments. Examples of coatingspigments that can be used include those provided by the Color Divisionof Ferro Corporation, 4150 East 56th St., Cleveland, Ohio 44101, andproduced using high temperature calcinations, including PC-9415 Yellow,PC-9416 Yellow, PC-9158 Autumn Gold, PC-9189 Bright Golden Yellow,v-9186 Iron-Free Chestnut Brown, V-780 Black, V0797 IR Black, V-9248Blue, PC-9250 Bright Blue, PC-5686 Turquoise, V-13810 Red, V-12600Camouflage Green, V12560 IR Green, V-778 IR Black, and V-799 Black.

In the initial step of the process of the present invention, porous baseparticles are provided. Particle synthesis allows properties of thealgae-resistant granules to be tailored, such as the porosity anddistribution of the algaecide, such as copper oxide. The base particlesare preferably prepared by mixing mineral particles with a suitablebinder, such as a binder comprising an aluminosilicate material, such asclay (which is also, formally, composed of “mineral particles,” but notas that term is used herein), as is shown schematically in FIG. 4. Themixture is then formed into base particles, using a forming process suchas press, molding, cast molding, injection molding, extrusion, spraygranulation, gel casting, pelletizing, compaction, or agglomeration.Preferably, the resulting base particles have sizes between about 500 μmand 2 mm.

As shown schematically in FIG. 4, the process of the present inventioncan employ a conventional extrusion apparatus 40. Kaolin clay, mineralparticles and water (to adjust mixability) can be charged to a hopper42, and mixed by a suitable impeller 44 before being fed to an extrusionscrew 46 provided in the barrel 48 of the extrusion apparatus. The screw46 forces the mixture through a plurality of apertures 50 having apredetermined dimension suitable for sizing roofing granules. As themixture is extruded, the extrudate 54 is chopped by suitable rotatingknives 52 into a plurality of base particles 60, which are subsequentlyfired at an elevated temperature to sinter or densify the binder.

In addition, the present process comprises providing at least oneinorganic algaecide on or within the base particle to formalgaecide-bearing particles. Preferably, in one embodiment of theprocess of the present invention, the at least one inorganic algaecideis mixed with the binder and the mineral particles before the mixture isformed into the base particles. In the alternative, or in addition, theformed base particles can be coated with a mixture of algaecide andbinder.

In another alternative, the base particles are formed from the mineralparticles and the binder, and fired at an elevated temperature toprovide inert, porous, fired base particles. The porous base particlescan then be treated with a solution of a soluble algaecide, such as anaqueous solution of a water-soluble copper salt, such as cupric nitrateor cuprous chloride, which is drawn into the porous base particles bycapillary action, to form algaecide solution-laden particles. Thesolution-laden particles can then be treated, as by drying. Optionally,the solution-laden base particles are treated to convert the solublealgaecide to a less soluble form. For example, when the solublealgaecide is a soluble copper salt, the solution-laden particles can betreated by heating to convert the soluble copper salt into a copperoxide, such as cuprous oxide, a less soluble inorganic algaecide.

Alternatively, the porous base particles can be mixed with a slurry ofalgaecide-forming compound, the slurry being drawn into the pores in thebase particles by capillary action to form slurry-laden particles. Theslurry-laden particles can then be subsequently treated to convert thealgaecide-forming compound into an inorganic algaecide.

The at least one algaecide is preferably selected from the groupconsisting of copper materials, zinc materials, and mixtures thereof.The copper materials can include cuprous oxide, cupric acetate, cupricchloride, cupric nitrate, cupric oxide, cupric sulfate, cupric sulfide,cupric stearate, cupric cyanide, cuprous cyanide, cuprous stannate,cuprous thiocyanate, cupric silicate, cuprous chloride, cupric iodide,cupric bromide, cupric carbonate, cupric fluoroborate, and mixturesthereof. The zinc materials can include zinc oxide, such as Frenchprocess zinc oxide, zinc sulfide, zinc borate, zinc sulfate, zincpyrithione, zinc ricinoleate, zinc stearate, zinc chromate, and mixturesthereof. Preferably, the at least one algaecide is cuprous oxide andzinc oxide.

The algaecide resistance properties of the algaecide resistant roofinggranules of the present invention are determined by a number of factors,including the porosity of the roofing granules, the nature and amount(s)of the algaecide employed, and the spatial distribution of the algaecidewithin the granules.

The process of the present invention advantageously permits the algaeresistance of the shingles employing the algae-resistant granules to betailored to specific local conditions. For example, in geographic areasencumbered with excessive moisture favoring rapid algae growth, thegranules can be structured to release the relatively high levels ofalgaecide required to effectively inhibit algae growth under theseconditions. Conversely, where algae growth is less favored by localconditions, the granules can be structured to release the lower levelsof algaecide effective under these conditions.

The algae resistance properties of the granule bodies can also be variedthrough control of the porosity conferred by the binder employed. Forexample, the binder porosity can be controlled by adjusting the ratio ofthe mineral particles and the aluminosilicate employed, as well as bythe heat treatment applied. Also, porosity can be induced by using anadditive that burns off or produces gaseous products that aresubsequently entrained in the structure of the granule bodies.

The porosity of the granule bodies can also be controlled by selectionof the shape and particle size distribution of the mineral particlesprovided. For example, by selecting mineral particles known to packpoorly, the porosity can be increased.

Combinations of the above-described alternatives for introducingalgaecide into and/or on the granule bodies can also be employed. Byadjusting the amount and selecting the type of algaecide used, and byadjusting the porosity of the granules, a variety of different algaecideleach rates and leaching profiles can be obtained.

For example, a first algaecide can be incorporated in the binder used toaggregate the mineral particles, and a second algaecide, less solublethan the first algaecide, can be introduced into pores formed in thegranule bodies. The spatial distribution of the first algaecide withinthe binder will tend to provide a lower leaching rate compared with thespatial distribution of the second algaecide, located in the pores, andtend to compensate for the difference in solubility, so that a desiredleach profile can be achieved.

FIGS. 1, 2 and 3 schematically illustrate examples of algae-resistantgranules prepared according to the process of the present invention andexhibiting three distinct morphologies. FIG. 1 schematically illustratesan algae-resistant granule 10 formed from a base particle A covered witha coating of a binder B in which are distributed algaecide particles C.The base particle A is formed from mineral particles bound together witha binder (not shown individually). This type of algae-resistant granule10 can be formed by initially preparing an inert base particle frommineral particles and binder as described above, and then covering thebase particle with a coating of binder containing algaecide.

FIG. 2 schematically illustrates an algae-resistant granule 20 formedfrom a base particle A having a plurality of pores P, the pores beingfilled with a binder B in which are distributed algaecide particles C.The base particle A is also formed from mineral particles bound togetherwith a binder (not shown individually). This type of algae-resistantgranule 20 can be formed by preparing a base particle from mineralparticles and binder containing algaecide.

FIG. 3 schematically illustrates an algae-resistant granule 30 formedfrom a base particle A having a plurality of pores P, the surfaces ofthe pores P having deposited thereon a plurality of algaecide particlesC. This type of algae-resistant granule 30 can be formed by initiallypreparing an inert base particle from mineral particles and binder asdescribed above, and then infiltrating the pores with an aqueoussolution of a water-soluble algaecide such as cupric nitrate, and thendrying the particle. When the algaecide is a water-soluble copper salt,such as cupric nitrate, the particle can be fired at an elevatedtemperature to convert copper salt successively to cupric oxide and thento cuprous oxide, which is advantageously less soluble than cupricoxide.

FIGS. 5 and 6 are electron micrographs of algae-resistant granulesprepared according to the process of the present invention showing poresand included copper oxide.

The algae-resistant granules prepared according to the process of thepresent invention can be employed in the manufacture of algae-resistantroofing products, such as algae-resistant asphalt shingles, usingconventional roofing production processes. Typically, bituminous roofingproducts are sheet goods that include a non-woven base or scrim formedof a fibrous material, such as a glass fiber scrim. The base is coatedwith one or more layers of a bituminous material such as asphalt toprovide water and weather resistance to the roofing product. One side ofthe roofing product is typically coated with mineral granules to providedurability, reflect heat and solar radiation, and to protect thebituminous binder from environmental degradation. The algae-resistantgranules of the present invention can be mixed with conventional roofinggranules, and the granule mixture can be embedded in the surface of suchbituminous roofing products using conventional methods. Alternatively,the algae-resistant granules of the present invention can be substitutedfor conventional roofing granules in the manufacture of bituminousroofing products to provide those roofing products withalgae-resistance.

Bituminous roofing products are typically manufactured in continuousprocesses in which a continuous substrate sheet of a fibrous materialsuch as a continuous felt sheet or glass fiber mat is immersed in a bathof hot, fluid bituminous coating material so that the bituminousmaterial saturates the substrate sheet and coats at least one side ofthe substrate. The reverse side of the substrate sheet can be coatedwith an anti-stick material such as a suitable mineral powder or a finesand. Roofing granules are then distributed over selected portions ofthe top of the sheet, and the bituminous material serves as an adhesiveto bind the roofing granules to the sheet when the bituminous materialhas cooled. The sheet can then be cut into conventional shingle sizesand shapes (such as one foot by three feet rectangles), slots can be cutin the shingles to provide a plurality of “tabs” for ease ofinstallation, additional bituminous adhesive can be applied in strategiclocations and covered with release paper to provide for securingsuccessive courses of shingles during roof installation, and thefinished shingles can be packaged. More complex methods of shingleconstruction can also be employed, such as building up multiple layersof sheet in selected portions of the shingle to provide an enhancedvisual appearance, or to simulate other types of roofing products.

The bituminous material used in manufacturing roofing products accordingto the present invention is derived from a petroleum processingby-product such as pitch, “straight-run” bitumen, or “blown” bitumen.The bituminous material can be modified with extender materials such asoils, petroleum extracts, and/or petroleum residues. The bituminousmaterial can include various modifying ingredients such as polymericmaterials, such as SBS (styrene-butadiene-styrene) block copolymers,resins, oils, flame-retardant materials, oils, stabilizing materials,anti-static compounds, and the like. Preferably, the total amount byweight of such modifying ingredients is not more than about 15 percentof the total weight of the bituminous material. The bituminous materialcan also include amorphous polyolefins, up to about 25 percent byweight. Examples of suitable amorphous polyolefins include atacticpolypropylene, ethylene-propylene rubber, etc. Preferably, the amorphouspolyolefins employed have a softening point of from about 130 degrees C.to about 160 degrees C. The bituminous composition can also include asuitable filler, such as calcium carbonate, talc, carbon black, stonedust, or fly ash, preferably in an amount from about 10 percent to 70percent by weight of the bituminous composite material.

The following examples are provided to better disclose and teachprocesses and compositions of the present invention. They are forillustrative purposes only, and it must be acknowledged that minorvariations and changes can be made without materially affecting thespirit and scope of the invention as recited in the claims that follow.

EXAMPLE 1

634 g of stone dust from rhyolite igneous rock (Wrentham, Mass.) aremixed for 20 minutes in a Hobart mixer with 1901 g of kaolin clay (CedarHeights Clay Co., Oak Hill, Ohio), 44 g of cuprous oxide (AmericanChemet Corporation, Deerfield, Ill.) and 2.2 g of Kadox—brand zinc oxide(Zinc Corporation of America, Monaca, Pa.). The mixture is then extrudedusing a single barrel extruder to form green granules having an averageparticle size of about 2.5 mm. The green granules are then fired in aBlue M periodic oven (Lunaire Limited, Williamsport, Pa.) at atemperature of 1050 degrees C. for 180 minutes.

EXAMPLE 2

The process of Example 1 is repeated, except that 500 g of the firedgranules are coated with a colorant mixture of 15 g of pigment particles(V-780, Ferro Corporation), 40 g of aqueous sodium silicate (40 percentby weight solids, having a Na₂O:SiO₂ ratio of 1:3.2), and 30 g of kaolinclay. 0.152 g of coating mixture are applied per g of granule. Thecoated granules are subsequently fired in a rotary kiln at 500 degreesC. for 20 minutes.

EXAMPLE 3

The process of Example 1 is repeated, except that 500 g of firedgranules are coated with an algaecide mixture of 17 g of cuprous oxide,1.1 g of zinc oxide, 60 g of the aqueous sodium silicate employed inExample 2, and 45 g of kaolin clay. 0.246 g of the algaecide mixture areapplied per g of granules to form algaecide-coated granules. Thealgaecide-coated granules are further coated with a colorant coatingmixture employed in Example 2, except that 6 g of pigment particles, 16g of sodium silicate, and 10 g of kaolin clay are used. The resultingcoated granules are subsequently fired in a rotary kiln at 400 degreesC. for 20 minutes.

EXAMPLE 4

The process of Example 1 is repeated, except that 500 g of the granulesare coated with an intermediate coating mixture of 20 g of the aqueoussodium silicate employed in Example 2, and 15 g of kaolin clay. 0.07 gof the intermediate coating mixture are applied per g of granules toform algaecide-laden granules. The algaecide-laden granules are furthercoated with a colorant coating mixture employed in Example 2, exceptthat 6 g of pigment particles, 20 g of sodium silicate, and 15 g ofkaolin clay are used. The resulting particles are subsequently fired ina rotary kiln at 500 degrees C. for 20 minutes.

EXAMPLE 5

634 g of stone dust from rhyolite igneous rock form Wrentham, Mass., aremixed with 1901 g of Cedar Heights Goat Hill Clay #30 and 422 g ofdeionized water in a Hobart mixer for 20 minutes. The mixture is thenextruded using a single barrel screw extruder through a die withplurality of holes and subsequently chopped into granules having anaverage particle size of about 2.3 mm. The green granules are then driedat 80 degrees C. overnight and fired in a periodic oven (manufacturer,Blue M) to a temperature of 1200 degrees C. for 3 hours.

EXAMPLE 6

2310 g of stone dust are mixed with 770 g of Cedar Heights Goat HillClay #30 and 420 g of deionized water in a Hobart mixer for 20 minutes.The mixture is then extruded using a single barrel screw extruderthrough a die with plurality of holes and subsequently chopped intogranules having an average particle size of about 2.3 mm. The greengranules are then dried at 80 degrees C. overnight and fired in aperiodic oven (Lindberg) to a temperature of 1120 degrees C. for 2hours.

EXAMPLE 7

72.64 kg of stone dust is mixed with 18.16 kg of KT Clay Tennessee SGPclay, 182 g of Allbond 200 Progel Corn Flour (Lauhoff Grain Company, St.Louis, Mo.), and 422 g of deionized water in a Lödige mixer (Gebr.Lödige Maschinenbau GmbH, Paderborn, Germany). The mixture is thenextruded using a piston extruder through a die with a plurality of holesand subsequently chopping into granules having an average particle sizeof about 1.78 mm. The green granules are then dried at 105 degrees C.overnight and fired in a rotary kiln set to a temperature of 1085degrees C.

EXAMPLE 8

The process of Example 7 is repeated, except that 500 g of the firedgranules are coated with an algaecide mixture of 17 g of cuprous oxide,0.9 g of zinc oxide, 16 g of the aqueous sodium silicate employed inExample 2, and 10 g of kaolin clay. 0.088 g of the algaecide mixture areapplied per gram of granule to form algaecide-coated granules. Thealgaecide-coated granules are further coated with a colorant coatingmixture as in Example 2 and the resulting coated green granules aresubsequently fired as provided in Example 2.

EXAMPLE 9

The process of Example 7 is repeated, except that after firing thegranules, 500 g of the granules are coated with a colorant mixture of 6g of pigment particles (V-780, Ferro Corporation), 16 g of the aqueoussodium silicate employed in Example 2, and 10 g of kaolin clay. 0.0064 gof coating mixture are applied per gram of granule. The coated granulesare subsequently fired as provided in Example 2.

EXAMPLE 10

352 g of stone dust are mixed with 352 g of Cedar Heights Goat Hill Clay#30 and 120 g of deionized water in a Hobart mixer for 20 minutes. Themixture is then extruded using a single barrel screw extruder through adie with plurality of holes and subsequently chopped into granuleshaving an average particle size of about 2.3 mm. The green granules arethen dried at 80 degrees C. overnight and fired in a periodic oven(manufacturer Blue M) to a temperature of 1100 degrees C. for 2 hours. Acopper nitrate solution was made with 100 g of copper nitrate dissolvedin 100 g of deionized water. Twenty-five grams of the fired granuleswere tumbled in Nalgene jar with 10 ml of the copper nitrate solution.The granules were separated from the remaining solution using a Büchnerfunnel and filter paper, and the granules are dried in an 80 degree C.drying oven overnight. The resulting granules contain about 6% by weightcopper nitrate. The copper nitrate laden granules are then fired to 1050degrees C. for 2 hours to convert the copper nitrate into copper oxide.Resulting granules are shown in the micrographs of FIGS. 5 and 6.

EXAMPLE 11

The process of Example 6 is repeated, except that the undried greengranules are shaken in a container with 3 g of cuprous oxide powder,effectively coating the surface of the granules with cuprous oxidepowder. The resultant undried green granules are subsequently dried andfired as provided in Example 6.

EXAMPLE 12

The process of Example 11 is repeated, except that cuprous-oxide ladengranules are coated using 500 g with a colorant mixture of 6 g ofpigment particles (V-780 Ferro Corporation), 16 g of the aqueous sodiumsilicate employed in Example 2, and 10 g of kaolin clay. 0.064 g ofcoating mixture is applied per gram of green granule. The coatedgranules are subsequently fired as provided in Example 2.

Various modifications can be made in the details of the variousembodiments of the processes, compositions and articles of the presentinvention, all within the scope and spirit of the invention and definedby the appended claims.

We claim:
 1. An algae-resistant roofing shingle, the shingle beingproduced by a process comprising producing algae-resistant roofinggranules, and adhering the granules to a shingle stock material, thealgae-resistant roofing granules being produced by a process comprising:(a) providing porous, inert base particles; and (b) providing at leastone inorganic algaecide on or within the base particles to formalgaecide-bearing particles.
 2. An algae-resistant roofing shingleaccording to claim 1, wherein the base particles are prepared from amixture including stone dust and a binder.
 3. An algae-resistant roofingshingle according to claim 2 wherein the binder comprises analuminosilicate material.
 4. An algae-resistant roofing shingleaccording to claim 3 wherein the mixture is formed into base particlesby a forming process selected from press molding, cast molding,injection molding, extrusion, spray granulation, gel casting,pelletizing, compaction and agglomeration.
 5. An algae-resistant roofingshingle according to claim 1 wherein the at least one inorganicalgaecide is provided on the base particle by coating the base particlewith the at least one inorganic algaecide.
 6. An algae-resistant roofingshingle according to claim 3 wherein the base particles are fired in akiln to insolubilize the binder.
 7. An algae-resistant roofing shingleaccording to claim 1 wherein the at least one inorganic algaecide isselected from the group consisting of copper materials, zinc materials,and mixtures thereof.
 8. An algae-resistant roofing shingle according toclaim 7 wherein the inorganic algaecides are cuprous oxide and zincoxide.
 9. An algae-resistant roofing shingle according to claim 7wherein the at least one inorganic algaecide is provided in the baseparticles after the base particles are fired, an algaecide-formingcompound being dissolved in a fluid to form a solution, the solutionbeing drawn into the pores in the base particles by capillary action toform solution-laden particles, the solution-laden particles beingsubsequently treated to convert the algaecide-forming compound to aninorganic algaecide.
 10. An algae-resistant roofing shingle according toclaim 9 wherein the algaecide-forming compound is a soluble copper salt,and the solution-laden particles are subsequently treated by heating theparticles to convert the soluble copper salt to cuprous oxide.
 11. Analgae-resistant roofing shingle according to claim 7 wherein the atleast one inorganic algaecide is provided in the base particles afterthe base particles are fired, an algaecide-forming compound being mixedwith a binder and a fluid to form a slurry, the slurry being drawn intothe pores in the base particles by capillary action to form slurry-ladenparticles, the slurry-laden particles being subsequently treated toconvert the algaecide-forming compound to an inorganic algaecide.
 12. Analgae-resistant roofing shingle according to claim 11 wherein thealgaecide-forming compound is a soluble copper salt, and theslurry-laden particles are subsequently treated by heating the particlesto convert the soluble copper salt to cuprous oxide.
 13. Analgae-resistant roofing shingle according to claim 1 further comprisingcoating the algaecide-bearing particles with a colorant composition. 14.An algae-resistant roofing shingle according to claim 13 wherein thecolorant composition includes a fusible binder, and further comprisingheating the colorant-coated algaecide-bearing particles to fuse thebinder.
 15. An algae-resistant roofing shingle, the shingle beingproduced by a process comprising producing algae-resistant roofinggranules, and adhering the granules to a shingle stock material, thealgae-resistant roofing granules being produced by a process comprising:(a) mixing stone dust, a binder and at least one inorganic algaecide;and (b) forming the mixture into particles by a forming process selectedfrom press molding, cast molding, injection molding, extrusion, spraygranulation, gel casting, and pelletizing.
 16. An algae-resistantroofing shingle according to claim 15 wherein the at least one inorganicalgaecide is selected from the group consisting of copper materials,zinc materials, and mixtures thereof.
 17. An algae-resistant roofingshingle according to claim 16 wherein the inorganic algaecides arecuprous oxide and zinc oxide.
 18. An algae-resistant roofing shingleaccording to claim 15, wherein the binder comprises an aluminosilicatematerial, and the process further comprises firing the particles in akiln to insolubilize the binder.